Body shape as a visual feature: evidence from spatially-global attentional modulation in human visual cortex

Feature-based attention supports the selection of goal-relevant stimuli by enhancing the visual processing of attended features. A defining property of feature-based attention is that it modulates visual processing beyond the focus of spatial attention. Previous work has reported such spatially-global effects for low-level features such as color and orientation, as well as for faces. Here, using fMRI, we provide evidence for spatially-global attentional modulation for human bodies. Participants were cued to search for one of six object categories in two vertically-aligned images. Two additional, horizontally-aligned, images were simultaneously presented but were never task-relevant across three experimental sessions. Analyses time-locked to the objects presented in these task-irrelevant images revealed that responses evoked by body silhouettes were modulated by the participants' top-down attentional set, becoming more body-selective when participants searched for bodies in the task-relevant images. These effects were observed both in univariate analyses of the body-selective cortex and in multivariate analyses of the object-selective visual cortex. Additional analyses showed that this modulation reflected response gain rather than a bias induced by the cues, and that it reflected enhancement of body responses rather than suppression of non-body responses. Finally, the features of early layers of a convolutional neural network trained for object recognition could not be used to accurately categorize body silhouettes, indicating that the fMRI results were unlikely to reflect selection based on low-level features. These findings provide the first evidence for spatially-global feature-based attention for human bodies, linking this modulation to body representations in high-level visual cortex.